1. Field of the Invention
The present invention relates to a screen printing apparatus.
2. Description of the Conventional Art
A screen printing apparatus is structured such as to move a squeegee along an upper surface of a screen mask and transfer a printing agent such as a creamed solder mounted on the screen mask or the like to a plate to be printed such as a printed circuit board or the like through a through hole formed in the screen mask so as to print.
Further, the screen mask mentioned above is held within a frame in a state of being tensed by a holding member made of a raw material having a slight elasticity such as a Tetron or the like.
Furthermore, the conventional screen printing apparatus is structured such that two squeegees are employed and are alternately moved in opposite directions so as to print.
Accordingly, extrusive forces in opposite directions are repeatedly applied to the screen mask, and an elasticity of the holding member does not become uniform after a long time use. Then, as a result, the screen mask generates a displacement. Consequently, there occur matters that it is impossible to accurately print on the basis of a pattern of the printed circuit board corresponding to the plate to be printed, and that an application amount of the printing agent lacks in uniformity.
Moreover, there is generated a problem that in the case that the printing agent such as the creamed solder or the like is exposed to an air so as to be oxidized, the printing agent is solidified and hardly taken out from the through hole in the screen mask in addition that a quality thereof is deteriorated.
The present invention is made by taking the points mentioned above into consideration, and an object of the present invention is to provide a screen printing apparatus which can print by means of only movement in one direction of a single squeegee, can prevent an oxidization of a printing agent as much as possible, and can solve all of the problems mentioned above.
Accordingly, in accordance with a content of the present invention, there is provided a screen printing apparatus comprising:
a printing agent sweeping drum which has a supporting shaft inserted through a center portion, freely rotates around the supporting shaft, oscillates along a moving direction of a squeegee via a movement of the supporting shaft by a supporting apparatus, moves downward at a movement starting end position, moves upward at a terminal end position, rotates at a predetermined angle in an opposite direction at a predetermined timing at the starting end position and the terminal end position, and has a lower end portion partly opened;
a squeegee holder which is arranged so as to be inclined at a predetermined angle within the printing agent sweeping drum and moves upward and downward at a predetermined timing;
the squeegee attached to a lower end portion of the squeegee holder; and
a printing agent extruding plate which is positioned at a front side in a forward moving direction of the squeegee.
Further, in the structure mentioned above, it is possible to close both end portions of the printing agent sweeping drum. With such an arrangement, it is possible to increase a sealing performance of the printing agent sweeping drum and it is possible to increase an oxidization preventing effect of the printing agent.
Further, in the case of closing both end portions of the printing agent sweeping drum so as to increase the sealing performance as mentioned above, the structure may be made such as to charge a nitrogen gas into the printing agent sweeping drum. In this case, it is possible to further improve the oxidization preventing effect of the printing agent. In particular, a significant effect can be obtained in the case that the printing agent is a tin or a copper.
Still further, in the structure mentioned above, it is possible to arrange a printing agent supplying apparatus within the printing agent sweeping drum. With such an arrangement, it is possible to quickly supply the printing agent within the sealed printing agent sweeping drum. Therefore, it is possible to further increase the oxidization preventing effect of the printing agent.
Moreover, the structures mentioned above may be combined so as to provide a screen printing apparatus comprising:
a printing agent sweeping drum which has a supporting shaft inserted through a center portion, freely rotates around the supporting shaft, oscillates along a moving direction of a squeegee via a movement of the supporting shaft by a supporting apparatus, moves downward at a movement starting end position, moves upward at a terminal end position, rotates at a predetermined angle in an opposite direction at a predetermined timing at the starting end position and the terminal end position, and has a lower end portion partly opened;
a squeegee holder which is arranged so as to be inclined at a predetermined angle within the printing agent sweeping drum and moves upward and downward at a predetermined timing;
the squeegee attached to a lower end portion of the squeegee holder;
a printing agent extruding plate which is positioned at a front side in a forward moving direction of the squeegee;
both end portions of the printing agent sweeping drum being closed;
a nitrogen gas being charged into the printing agent sweeping drum; and
a printing agent supplying apparatus arranged within the printing agent sweeping drum,
wherein a vertical plate with which a back surface of the squeegee is slidably in contact is mounted to a front surface of the printing agent supplying apparatus, a step portion for forming a gap by which one end of a lower end open portion of the printing agent sweeping drum enters between a back surface lower end portion of the plate and the screen mask is provided in the back surface lower end portion of the plate, the lower end open portion of the printing agent sweeping drum is made small, an end portion in a forward moving direction side of the squeegee in the lower end open portion is at a position surrounding a part of the printing agent existing between the squeegee and the printing agent extruding plate and on the other hand an end portion in an opposite side of the lower end open portion is at a position entering into the gap between the plate and the screen mask at a time of printing, and the end portion in one side of the lower end open portion is at a position being in contact with the plate and on the other hand the end portion in an opposite side is within the gap between the plate and the screen mask at a time of finishing the printing. Accordingly, a sealing performance of the printing agent sweeping drum is further improved, and it is possible to further improve the oxidization preventing effect by the nitrogen gas.